1. Field of the Invention
The present invention relates to a method of transmitting and receiving image data which is suitably embodied in, for instance, a color copying machine or the like, in which original reading data comprises pixel data of respective colors such as R (red), G (green), and B (blue) and the image data has a time-dependent space area for K (black) data which is produced at the output stage. The invention also relates to an apparatus which is used in such a method.
2. Related Background Art
Ordinarily, in a color copying machine or the like, image signals of the respective colors of R (red), G (green), and B (blue) are produced in the image reading unit by using a reading sensor, such as a CCD. The image signals are converted into the image signals of C (cyan), M (magenta), and Y (yellow) as complementary colors of R, G, and B by predetermined image processing circuits. An image is formed on the basis of the image signals. At this time, there is a problem such that black cannot be clearly expressed, even mixing the color materials of C, M, and Y. Therefore, in an image printing unit, there is used a method whereby an image signal of black is produced from the three color signals of R, G, and B in addition to the image signals of C, M, and Y. A clear image is printed by using materials of four colors including for example, a black ink or toner in correspondence to the black image signal.
According to such a method, generally, the time-dependent areas to transmit and receive the image signals of four colors in the image printing unit are also assured even when the image data of R, G, and B are transmitted.
A color copying machine 16 using the above method will now be described with reference to a block diagram of FIG. 1.
Image signals which are obtained by reading an image by an image sensor 1 are output as four kinds of signals of R, G, B, and X. In this case, X denotes a blank signal indicative of a time-dependent area to transmit and receive black data which is produced by a black data producing circuit (UCR) 8 at the output stage.
That is, the data of one pixel is output in a form such as to time-sequentially include four signals of (R, G, B, X).
An output of the image sensor 1 is an analog signal and is amplified by an amplifier 2 at the output stage having a predetermined gain for every color. The amplified signal is then converted into a digital signal by an A/D converter 3 at the next stage.
Although each dot of the image sensor 1 ideally generates the same electrical output for a certain light intensity, there is actually a variation among the respective dots. To prevent the occurrence of a variation in light and dark images upon printing of an image due to a variation of the image sensor 1, a shading circuit 4 is provided at the next stage, thereby correcting an output variation of the image sensor 1.
A black character processing circuit 5 at the next stage extracts the portions of black characters in the read original. A black character area signal which is output from the processing circuit 5 is used in a black character conversion circuit 14 at the output stage. In the example of FIG. 1, an image editor unit 17 can be connected as an external apparatus through an I/F cable 18. The image editor unit 17 mainly has two functions and has two circuits 17a and 17b to realize those functions. The color conversion circuit 17a realizes a color converting function such as to change, for instance, a yellow image into a red image. The area control circuit 17b realizes an area control function to execute a predetermined process for an area which is designated by using a digitizer (not shown) provided for the image editor unit 17. The image editor unit 17 is used, for instance, in the case where a certain area in an original is erased or where only a certain area in an original is converted into a blue image. In the case where the image editor unit 17 is not used, an output or a black character processing circuit 5 is given to a variable multiplication processing circuit 6.
The image data from the image editor unit 17 is variably magnified into a desired size by the processing circuit 6.
practically speaking, for example, in the case of enlarging, the same data is read out a plurality of times. In the case of reducing, the image data is thinned out in accordance with a reduction ratio.
Although the image data which is input to and output from each of the circuits 1 to 6, 17a, and 17b mentioned above is the luminance data which is obtained by converting a reflected light, of the light which was irradiated onto an original, into an electric signal, density data is needed to print.
Therefore, the luminance data from the variable multiplication processing circuit 6 is converted into the density data by a LOG converter 7. On the other hand, the LOG converter 7 converts the luminance data into the data indicative of C, M, and Y by the bit inverted data of the data indicative of R, G, and B. The UCR 8 at the next stage produces black data on the basis of the data of C, M, and Y. As mentioned above, the image data does not include the black data until the circuits before the UCR 8. The image data includes the black data in the UCR 8 and subsequent circuits (such image data is shown by blank arrows in the diagram).
A masking circuit 9 executes a correcting process according to the characteristics of the image sensor 1 and of the toner which is used in a printing unit 15. A density conversion circuit 11 executes a density converting process of each color in accordance with the operation of an operating unit (not shown). On the other hand, a binarization processing circuit 12 executes a binarizing process based on a dither method, an error diffusion method, or the like.
In such a color copying machine, for instance, a black character area signal which is produced by the black character processing circuit 5 in FIG. 1 is sent to the black character conversion circuit 14 at the output stage synchronously with the image signal.
On the other hand, a plurality of area signals generated from the image editor unit 17 are also sent to the post stage synchronously with the image data.
Further, a photograph control signal which is generated in the case of partially processing as a photograph is used in a character photograph processing circuit 10 at the post stage. In the case of partially erasing or leaving an image, one of the area signals is used in a trim mask circuit 13.
In addition to the above signals, a negative/positive signal, a character synthesis signal, and the like (not shown here) are also included as various kinds of image control signals which are produced by the image editor unit 17.
As mentioned above, there are a plurality of kinds of image control signals to be transmitted synchronously with the image. There is a problem such that when those signals are transmitted and received via the I/F cable 18, the number of terminals of the connectors and the number of poles of the cables are increased, so that the costs rise.
On the other hand, since the image control signals relate to the image processing contents to be executed for every pixel, the image control signals need to be synchronized with the image data. Therefore, the image control signals must be delayed by only the time which is required to execute an image process such as color conversion, area control, or the like in the image editor unit 17. Accordingly, a delay circuit 17c must be provided for the image editor unit 17. There is also a problem such that a circuit construction becomes complicated. Such a problem also occurs even in the case where the image editor unit is not connected as shown in FIG. 1. That is, in more general, as shown in FIG. 2, in the case where image data which was read by an image reading unit 101 is subjected to an image process to form image control signals by an image processor 102 and is further subjected to an image process using the image control signals by an image processor 104 through an image processor 103, the image control signals must be delayed by only the time which is required for the image process which is performed by the image processor 103. For this purpose, a delay circuit 105 is provided and it is necessary to synchronize the image data and the image control signals. In such a case, the circuit construction also becomes complicated.